Gaucher's disease is an inborn error of sphingoglycolipid metabolism which, although always associated with glucocerebrosidase deficiency and accumulation of glycocerebroside in reticuloendothelial organs, demonstrates marked clinical variability. The intent of this project is to derive clinical, biochemical and genetic data from a large series of patients with Gaucher's disease in order to evaluate: 1. the natural history, effect of splenectomy, abnormalities of leukokinetics, immunoglobulins and coagulation factors, and a possible association with development of immunoproliferative and myeloproliferative diseas. 2. the reliability of different enzyme assay procedures for biochemical diagnosis, and the correlation between enzyme deficiency and clinical severity of disease, information essential for valid genetic counselling. 3. the feasibility of in vitro replenishment with exogenous gluococerebrosidase of enzyme-deficient Gaucher fibroblasts in culture.